Modesto ADU Rules & Land Use Law: Size, Setbacks, Parking & Permits

ADU Regulations in Modesto, California

Updated September 29, 2026

Modesto's ADU rules sit in the city's own land use code — Title 10, Chapter 4, Article 5 of the Modesto Municipal Code, added by Ordinance 3762-C.S. and amended in 2025. Modesto is an incorporated charter city, so Stanislaus County's ADU chapter (21.74) does not apply inside the city limits; the county's rules govern unincorporated land only, although its free ADU plan sets are accepted in Modesto.

Below is a summary of the key zoning rules applicable to Accessory Dwelling Units in Modesto as of 2026. Regulations are governed by the Modesto Municipal Code Title 10, Chapter 4, Article 5, sections 10-4.501 to 10-4.512, which implements California Government Code sections 66310 to 66342.

Additional Local Requirements for Modesto

• Up to 2 additional units on a single-family lot — any combination of attached, detached or converted ADU plus one JADU; three homes counting the main house
• ADUs are allowed in single-family, multifamily and mixed-use zones; JADUs only in single-family zones where a house exists or is proposed
• Detached ADU height: 16 ft, or 18 ft within 1/2 mile of a major transit stop, plus 2 ft for an aligned roof pitch; attached ADUs up to 25 ft and two storeys
• Approval is ministerial with no public hearing, and the city must decide within 60 days or the ADU is deemed approved
• No impact fee on an ADU under 750 sq ft; larger ADUs are charged proportionally to the main home
• Building permit fee: $2,429 per permit for ADUs and small dwellings up to 1,200 sq ft under the FY 2026-27 fee schedule, including mechanical, plumbing and electrical
• Photovoltaic (solar) plans are required for new-construction detached ADUs under the California Energy Code
• Fire sprinklers cannot be required in the ADU unless the main home needs them, and no passageway may be required
• Rentals must be for 30 days or more, and the JADU cannot be sold separately from the main house
• The City Council may designate areas where ADUs are not allowed because of water or sewer infrastructure constraints

Which law applies to a Modesto ADU: city, county or state?

All three, in this order. Modesto's own code governs first: the city is incorporated, so the rules that count inside the city limits are Title 10, Chapter 4, Article 5 of the Modesto Municipal Code (sections 10-4.501 to 10-4.512), not Stanislaus County's Chapter 21.74. Where a local standard conflicts with California Government Code section 66310 et seq., state law applies — section 10-4.512 says so directly.

One practical consequence: the county publishes free ADU plan sets (405 sq ft, 744 sq ft and 1,192 sq ft, drawn to the 2025 California Building Code) that can be used in Modesto as well as in the unincorporated county. For a new-construction detached ADU, those drawings can remove most of the design cost before you ever speak to a plan reviewer.

How many ADUs can I build in Modesto?

• Single-family lot: up to two additional units — any combination of attached, detached or converted ADU, plus one JADU.
• Multifamily building: ADUs inside existing non-livable space can be at least one and up to 25% of the existing units; up to 8 detached ADUs on a lot with an existing multifamily building, and up to 2 detached ADUs where the multifamily building is proposed.
• Places of worship: up to two detached ADUs of no more than 1,200 sq ft each, with 4 ft interior side and rear setbacks and no extra parking where one existing space is reserved per ADU.

California also requires Modesto to approve certain ADU types ministerially, and the city's code says so explicitly in section 10-4.511. Those units cannot be refused because the property has non-conforming zoning conditions, and correcting those conditions cannot be made a condition of approval.

Modesto ADU size, height and setback limits

Parking in Modesto: one space maximum, none in six cases

Modesto cannot require more than one off-street space for an ADU, and a tandem space in an existing driveway counts. Uncovered spaces may sit in the required front setback where a driveway already exists, or in the rear setback where the lot has alley access. No space at all may be required in these six situations:

• the ADU is within 1/2 mile walking distance of public transit;
• it is in an architecturally or historically significant district;
• it is part of the main residence or an existing accessory structure;
• the street requires permits but no permit is offered to the ADU occupant;
• a car-share vehicle is available within one block;
• the ADU permit is filed together with a new single-family or multifamily dwelling permit on the same lot.

Parking that disappears when a garage or carport is demolished or converted does not have to be replaced.

Modesto's ADU Express program: same-day plan review

Modesto runs an appointment-based ADU Express service that coordinates Building Safety, Fire, Planning and Engineering in one review session for ADU and JADU projects that qualify for ministerial approval. Same-day approval requires plans prepared by a professional designer, licensed architect or engineer. Appointments are booked through Building Safety at 209-577-5232, extension 0; the program's flyer lists Tuesday sessions from 10:00 to 11:00 a.m.

The city describes an eight-step path: create a plan, get planning advice, prepare the submittal package, apply through the eTRAKiT portal, hire licensed professionals, go through staff plan review, receive the permit, then build and inspect. Housing questions go to the Community Development Division at housing@modestogov.com or 209-577-5211; planning questions to 209-577-5267.

What a Modesto ADU costs: $2,429 per permit

The FY 2026-27 Building Safety fee schedule charges $2,429 per permit for accessory dwelling units and small dwellings up to 1,200 sq ft, covering mechanical, plumbing and electrical work, payable at application. On top of that, no impact fee applies to an ADU under 750 sq ft, and above that threshold fees must be charged in proportion to the main dwelling's square footage — not at the full rate for a new house.

Financial help exists: CalHFA's ADU grant programme has offered up to $40,000, and local options include the Valley First Credit Union Expand.Enhance.Empower loan programme and Stanislaus Equity Partners. Beware of older guides quoting Modesto's "ADU Development Fees 2022-2023" document — that link is dead and the numbers are obsolete.

Conversions, as-built drawings and unpermitted space

If you are converting a garage, a workshop or an unpermitted living area, Modesto does not require a setback beyond what fire and safety need, allows expansion of up to 150 sq ft of the existing structure for ingress and egress, waives lot coverage limits for units of 800 sq ft or less, and prohibits the city from requiring you to correct non-conforming zoning conditions as a condition of approval.

What reviewers will still need is a clear picture of how the structure actually exists today — that is what a conversion set of drawings has to document. California law also prevents the city from denying a permit because of building-code violations or unpermitted structures, as long as the ADU itself is built to code.

Frequently Asked Questions About ADUs in Modesto

Are ADUs allowed in Modesto?

Yes. Modesto allows ADUs in any zone that permits single-family, multifamily or mixed-use development, and JADUs in single-family zones where a house exists or is proposed. Approval is ministerial with no public hearing, and the city must decide within 60 days of a complete application or the permit is deemed approved.

What is the maximum ADU size in Modesto?

A detached ADU can be up to 1,200 sq ft and can never exceed the floor area of the main home. An attached ADU is capped at 50% of the main home's floor area, but the code states that cap cannot be used to refuse an attached ADU of up to 800 sq ft. A JADU is limited to 500 sq ft inside the walls of the house.

What are Modesto's ADU setback and parking requirements?

A new detached ADU needs a minimum 4 ft side and 4 ft rear setback; a structure converted into an ADU only needs enough clearance for fire and safety. Parking is capped at one off-street space per ADU, and no space may be required when the unit is within 1/2 mile of transit, in a historic district, inside the main or accessory structure, on a permit-only street where the ADU occupant cannot get a permit, within a block of a car-share vehicle, or built together with a new dwelling permit on the same lot.

What does Modesto land use law say about ADUs?

ADUs are governed by the Modesto Municipal Code Title 10, Chapter 4, Article 5, sections 10-4.501 to 10-4.512. That article sets where ADUs are allowed, the size and height limits, setbacks, parking, the JADU owner-occupancy deed restriction and the fee rules, and it says that where a local standard conflicts with California Government Code section 66310 et seq., state law applies. It is a city code, not a county one: Stanislaus County's Chapter 21.74 has no force inside Modesto's city limits.

Does Modesto require a minimum ADU size?

No. Modesto's code sets no minimum floor area for an ADU, and California law forbids a minimum that would prevent an efficiency unit. Guides quoting a 150 sq ft minimum for Modesto are not supported by the current code.

How much does a Modesto ADU permit cost?

$2,429 per permit for an ADU or small dwelling up to 1,200 sq ft under the FY 2026-27 fee schedule, including mechanical, plumbing and electrical, payable when you apply. Separately, no impact fee applies to an ADU under 750 sq ft, and larger units are charged proportionally to the main home rather than at full new-house rates.

Can I convert my garage into an ADU in Modesto?

Yes. A conversion inside or replacing an existing structure needs only enough setback for fire and safety, may expand the structure by up to 150 sq ft for ingress and egress, is exempt from lot coverage limits up to 800 sq ft, and the lost parking does not have to be replaced.

Do I have to live in the property to rent out a Modesto ADU?

No for an ADU — Modesto does not require owner occupancy for ADUs, and state law bars the requirement. A JADU is different: before final inspection the owner must record a deed restriction agreeing to live in the JADU or the rest of the house at all times, unless the owner is a government agency, land trust or housing organisation. Rentals must run 30 days or longer.

How long does a Modesto ADU permit take?

Ministerial review must be completed within 60 days of a complete application, and if the city takes no action the ADU is deemed approved. Modesto also runs ADU Express, an appointment-based session that reviews an eligible ADU with Building Safety, Fire, Planning and Engineering at once and can approve it the same day when the plans are prepared by a licensed professional.

Sources

• Modesto Municipal Code Title 10, Ch. 4, Art. 5 — Accessory Dwelling Units (Municode)
• City of Modesto — Accessory Dwelling Units program page
• City of Modesto — ADU Express flyer (PDF)
• City of Modesto — Building Safety fees (FY 2026-27)
• California Government Code Chapter 13 — Accessory Dwelling Units (sections 66310 to 66342)
• HCD — ADU Handbook (January 2025)
• Stanislaus County — ADUs and free plan sets (unincorporated areas; plan sets usable in Modesto)